Propylene polymer resins have enjoyed significant growth in recent years. In addition to propylene homopolymer, numerous copolymers with ethylene and other alpha-olefins are commercially produced. These include random copolymers, block copolymers and multi-phase polymer systems. This latter group of resins includes the so-called impact co-polymers and thermoplastic elastomers (TPEs), which contain a continuous phase of a crystalline polymer, e.g., highly isotactic polypropylene homopolymer, and those having a rubbery phase, e.g., ethylene-propylene copolymer.
These resins are widely used for extrusion for the production of films, fibers, and a range of molded goods, such as bottles, hoses and tubing, automobile parts and the like. While it is necessary that these resins have sufficiently low melt viscosity under conditions of high shear encountered in the extruder, the resin must also have sufficient melt strength after extrusion to prevent sagging or distortion of the extrudate before it is cooled below the melt point. High melt strength resins are particularly advantageous for the production of large thermoformed and blow molded articles, as well as foam and extruded sheets.
Isotactic Polypropylene (IPP) has become one of the most widely used commercial polymers because of its many desirable and beneficial physical properties such as low density, high melting point, high mechanical strength and chemical resistance. However, commercial PP is made up of linear molecules, and hence this material has relatively low melt strength and exhibits no strain hardening behavior in melt state. The linear molecular structure of PP is a direct result of the stereo-regulating catalyst (Ziegler-Natta catalyst) used for its production. Thus its uses have been limited in applications requiring high melt strength (Hmelt strength), such as blow molding, foaming and thermoforming. Therefore, the development of Hmelt strength-PP through incorporation of long chain branching has gained high importance in the past one decade.
Polypropylene has become more and more attractive for many different commercial applications. One reason might be that new developed processes based on single-site-catalyst systems open the possibility to tailor new polypropylenes for demanding end-applications, which has been not possible for a long time. Quite often such new polypropylenes based on single-site-catalyst systems are employed in case materials with a high stiffness are required. Moreover the amount of xylene soluble compared to conventional Zieglar-Natta products can be significantly lowered which opens the possibility to use polypropylene in niche areas as in the field of medicine or food packaging. However another factor that must be considered when developing new materials is whether they can be produced with reasonable effort. High output rates along with a minimum of energy requirement are appreciated (inter alia the polypropylene shall be formable at low temperatures). However, normally better process properties are at the cost of inferior solid state properties. Thus it is always required to achieve a balance between processability and end-product properties. Up to now there is still the need to develop polypropylenes which can be used in high demanding applications requiring good mechanical properties as high temperature resistance and stiffness, as well as high levels of purity. On the other hand said polypropylenes shall be easily processable.
Mechanistically, the reactivity of PP stems from its hydrogen atoms along the hydrocarbon skeleton that are subjected to free radical attack. The free radicals generated either by peroxide decomposition or in air/oxygen atmosphere, abstract the labile proton on the tertiary carbon sites. The macro radicals of PP will undergo either degradation leading to chain cleavage by β scission or grafting. Furthermore, due to the high instability of tertiary macro radicals, the degradation process is extremely fast at high temp. (T>Melting temperature). Thus stabilizing & consuming macro radicals in favor of grafting are the means to reduce the chain degradation. It is necessary to build the branched molecular structure from linear molecules that are destroyed by scission via a PFM. The envisaged chemical modification must favor the grafting reaction between the polymer chains over the β scission reaction. Another difficulty of free radical grafting arises from the competition between monomer grafting & homo polymerization. But this has been resolved in this invention by careful manipulation of process variables using relatively low dose acrylic based poly functional modifier.
Efforts to achieve the aforementioned objectives find mention in the art. One of such methodologies is introduction of branches into linear PP to produce “high melt strength PP(H-MS-PP)” having enhanced processability. Basically, branched PP is produced by subjecting PP to treatments which cleave chains, creating free radicals, & subsequently controlling the recombination of these chain fragments through kinetic & other process variables namely time, temperature, chemical environment etc. Tailoring the level of branching for specific applications involves controlling the branching process, compounding a branched PP (bPP) component into an appropriate linear PP either homo-PP/random or heterophasic copolymer (R-PP or PP-ICP) alone or both in a master batch or direct in situ situation. Whichever route is chosen, the finished resin largely retains the solid phase properties of the main PP components. These and other objectives of making long chain branched PP (LCB-PP) by a direct simple & cost effective reactive extrusion process has been focus of research by the present inventors, who have come up with novel solutions for achieving the said objectives.
Several methods have been used for increasing the melt strength of polypropylene, including oxidation and radiative treatments. The introduction of long chain branching (LCB) has also been used as highlighted in current patent & non-patent literature as for example, U.S. Pat. No. 6,306,970 B1; WO2007100436; Polymer Engineering & science, p-1339-13444, 2008; Macromolecules, Vol-37, p-9465, 2004; Polymer, Vol 47, p-7962-7969, 2006; Korea-Australia Rheology Journal Vol-11, No-4, December p-305-311, 1999. However, such methods typically require additional process steps beyond the steps required for the polymerization reaction. These additional steps pose several inconveniences including decreased processing efficiency and increased processing cost. Accordingly, it would be desirable to produce a high melt strength polypropylene by more convenient and less costly means.
Compared with a linear polymer having the same molecular weight, a long chain branch polymer shows high shear sensitivity, zero shear viscosity; melt elasticity, and high impact strength (Grassley, Ace. Chem. Res. 1977, 10, 332; Bersted, et al. J. Appl. Polym. Sci. 1981, 26, 1001; Roovers, Macromolecules 1991, 24, 5895). LCB polymers exhibit higher melt viscosities at low shear rates and lower viscosities at high shear rates. Shear thinning is advantageous in polymer processing, such as under high shear conditions. Further, high melt strength, i.e. increasing resistance to stretching during elongation of the molten material, is a desirable mechanical property which is important for thermoforming, extrusion coating, and blow molding processes involving predominately elongation flows.
U.S. Pat. No. 4,916,198 discloses a process of making high melt strength PP via irradiation process where oxygen concentration is controlled during ionic radiation exposure. In fact, it is believed that most of the reaction (chain scission) is restricted in the amorphous regions during solid-state modification & require thermal exposure of the irradiated polymer (as solid) so as to deactivate the available macro free radicals in the irradiated polymer either by fluidized bed process or melt kneading.
However, because the irradiation results in chain scission, even though there is recombination of chain fragments to reform chains, as well as joining of chain fragments to chains to form branches, there can be a net reduction in weight average molecular weight between the starting material and the end product, the desired substantially branched, high molecular weight, propylene polymer material. The cross-linked fraction of material is known to cause gelling in the products of thin cross-sections and also causes imbalance in the required mechanical properties. Objective is to develop the polymer which has the characteristics of strain hardening—thus with improved neck-in and sagging.
U.S. Pat. No. 6,774,186 discloses a free radical coagent which is a monomer or low molecular weight polymer having two or more functional groups with high response to free radicals. Typically, these functional groups are methacrylate, allyl or vinyl types. The free radical from peroxides enhances the rheological modification. Firstly, by peroxide induced allylic hydrogen abstraction from the co agent, a lower energy state, longer-lived free radical is created. This free radical can then induce branching in the ethylene elastomer by hydrogen abstraction. Due to the lower energy state of the free radical, beta-scission and disproportionation of either polypropylene or ethylene elastomer phase is less likely to occur. Secondly, the multifunctional co agent can act as a bridging group between the polymer chains. Suitable free radical coagents for this application would include diallyl terephthalate, triallylcyanurate, triallylisocyanurate, 1,2 polybutadiene, divinyl benzene, trimethylolpropane trimethacrylate, polyethylene glycol dimethacrylate, ethylene glycol dimethacrylate, pentaerythritol triacrylate, allyl methacrylate, N N′-m-phenylene bismaleimide, toluene bismaleimide-p-quinone dioxime, nitrobenzene, diphenylguanidine. Preferred coagents are triallylcyanurate, 1,2 polybutadiene, divinyl benzene, and trimethyolpropane trimethacrylate. The coagent is suitably present in an amount that is within the range of about 100 to 10,000 parts per million by weight. The range is desirably from about 500 to 5,000 parts, preferably from 1,000 to 3,000 parts per million by weight.
The peroxide and free radical co agent can be added by any conventional means. Illustrative procedures include imbibing it onto polymer pellets prior to compounding, adding it to polymer pellets as the pellets enter a compounding apparatus such as at the throat of an extruder, adding it to a polymer melt in a compounding apparatus such as a Haake, a Banbury mixer, a Farrel continuous mixer or a Buss-co-Kneader or injecting it into an extruder, at 100% active ingredients (i.e., neat) or optionally as a dispersion or solution in an oil, such as a processing oil, at a point where the extruder contents are in molten form. A preferred procedure is imbibing the peroxide and coagent into the polymer pellets prior to compounding.
Furthermore, despite intense interest and many research attempts, so far there is no known commercial process based on polymerization or direct chemically solid state post modification for preparing long chain branched polypropylene (LCB-PP). In a direct polymerization process, one major difficulty of in situ preparing LCB-PP polymers is due to the complicated PP macro monomer structures. There are two possible monomer insertion modes (including 1,2- and 2,1-insertions) and multiple chain termination mechanisms that can lead to polypropylene with various chain ends (Weng, et al. Macromol. Rapid Commun. 2000, 21, 1 103), while only the vinyl chain end is effective for LCB formation. Furthermore, the preparation of the most important isotactic polypropylene requires iso-specific catalysts, such as rac-Me2Si[2-Me-4-Ph(Ind)]2ZrCl2/MAO, which have limited special opening at the active site for incorporating macro monomers. Therefore, it is extremely difficult to find a catalyst system that can accommodate all the requirements, namely in situ formation of a significant amount of vinyl-terminated PP macro monomers and further incorporation of macro monomers into LCB-PP structure. In addition, under some reaction conditions, a small portion of the incorporated diolefin units might engage double enchainment, and the increase of cross-over structures in the polymer results in unprocessible (cross linked) polymer network. Thus, there is a continuing need for LCB polymers as well as methods and reagents for use in their synthesis.
The study reported in Macromolecules, 2001, 34 (17), pp 6056-6063 shows the effectiveness and its important role of a long relaxation time mode in order to enhance melt properties of PP. An introduction of long chain may be the exceptional methodology to obtain excellent melt properties without any disadvantages such as decompositions, aggravation of physical properties, etc. The PP with enhanced melt properties will find applications such as foaming, blow molding, thermoforming, and so on. The points made so far about an introduction of small amounts of ultra high molecular weight polymer could apply in principle to any polymer. Recently, considerable progress has been made in polymer dynamics and precision polymerization. This study would be also expected as a guiding principle in designing new materials with desirable processability.
WO/1994/007930 discloses processes for producing novel polyolefin polymers, and applications thereof. The structural features of polyolefin's that are considered most significant are molecular weight, which is related to polymer chain length, the type and tacticity of side-chain branches, and the distribution of side-chain branches along the main polymer chains. The random nature of most polymerization processes results in a heterogeneous polymer, rather than a truly homogeneous polymer product. Polyolefins produced by classical Ziegler-Natta catalysts consist of mixtures of molecules of different molecular weights and different amounts of comonomer incorporation. These differences result from the differences in catalysts used, and differing rates of comonomer incorporations. Other factors influencing polymer products include choice of monomers, catalyst reactivity or ability to incorporate co monomers, and differing polymerization process conditions.
WO/2004/046208 discloses a method for producing branched polypropylenes having improved processability and good mechanical strength. On the other hand, WO/1994/007930 relates to a process for preparing polypropylene and its copolymers having high melt strength. More specifically; the present invention relates to a process for preparing polypropylene and its copolymers, having high strength to shear free flow in the melt, while maintaining melt flow index suitable to processing.
EP1380613 discloses a process of producing polypropylene having increased melt strength by irradiating polypropylene in pellet form with an electron beam having an energy of from 0.5 to 25 MeV, delivered by an accelerator having a power of from 50 to 1000 kW and with a total radiation dose of from 10 to 120 kGray, characterised in that the irradiation is carried out in the presence of air.
U.S. Pat. No. 6,632,854 discloses an irradiation based process for production of polypropylene having improved properties via melt grafting of a coagent for forming long chain branches on the polypropylene molecules. Further more, U.S. Pat. No. 6,699,919 discloses a process of modifying Polypropylene having enhanced long chain branching and increased melts strength via grafting of modifier to generate long chain branches on to the polypropylene matrix. However this process is complex requiring accurate performance of multiple steps which makes the process cumbersome to implement in the industry.
EP0634441 discloses is a normally solid, high molecular weight, non-linear, substantially gel-free, propylene polymer material characterized by high melt strength due to strain hardening which is believed to be caused by free-end long chain branches of the molecular chains forming the polymer. Further disclosed is the use of the strain hardening polymer in extensional flow operations such as, for example, extrusion coating, film production, foaming and thermoforming.
For example, EP190,889A and U.S. Pat. No. 5,541,236A disclose a process for irradiating polypropylene to increase the melt strength thereof. It is disclosed that a linear propylene polymer material is irradiated under nitrogen with high energy ionizing radiation, preferably an electron beam, at a dose rate in the range of about 1 to 1×10 <4> Mrads per minute for a period of time sufficient for the appearance of long chain branching concomitantly with chain scission, but insufficient to cause gelation of the material. Thereafter, the material is maintained under the same inert environment, for a period of time sufficient for a significant amount of long chain branches to form. Finally, the material is treated to deactivate substantially all free radicals present in the irradiated material.
There are also some reports on the direct synthesis of long chain branched PP: using metallocene catalysis either directly or via the addition of pre-made PP macro monomers; using conjugated diene monomers; via the metallocene-mediated polymerization of PP in the presence of T-reagent p-(3-butenyl) styrene (Macromolecules 1999; 32:8678-80 & Macromolecules 2007; 40:2712-20).
U.S. Pat. No. 6,770,697 discloses a novel process of making high melt strength Polyolefin composition using master batch organo-clay in polyolefin. Applications include thermoforming, blow molding, foaming and spinning. Further, WO/2006/007512 describes a one pot process & reagent for producing long chain branched PP wherein in claim-3, long chain branched polypropylene has a melting temperature higher than 140° C.
A preferred multistage process is a “loop-gas phase”-process, such as developed by Borealis AIS, Denmark (known as BORSTAR® technology) described e.g. in patent literature, such as in EP 0 887 379 or in WO 92/12182. Multimodal polymers can be produced according to several processes which are described, e.g. in WO 92/12182, EP 0 887 379 and WO 97/22633. A multimodal polypropylene according to this invention is produced preferably in a multi-stage process in a multi-stage reaction sequence as described in WO 92/12182. The contents of this document are included herein by reference.
The electron beam irradiation of linear PP has been used to prepare PP with long chain branches or PP-Hmelt strength, as disclosed in PCT91/13933. The radiation leads to a hydrogen abstraction and under optimum reaction conditions-inert atmosphere and low temperature—the radical combination leads to formation of long chain branches. For example, the weight-average molecular mass is 298000 before irradiation with a 6 Mrad electron beam and 125000 after U.S. Pat. No. 5,605,936. Lucas et. al. have investigated the cross-linking of a propylene-ethylene random copolymer irradiated with a γ or an electron beam of ionizing radiation in air (U.S. Pat. No. 5,439,949). The efficiency of cross-linking was determined by refluxing in boiling xylene for 12 h. The gel content goes to 7.1 wt % with 10 M rad γ-radiation. Saito and coauthors have studied the cross-linking of PP irradiated with an electron beam under nitrogen in the presence of 1,6-hexanediol diacrylate used as coagent (U.S. Pat. No. 5,560,886).
In a European patent, Braga and Ghisellinii have obtained a mixture of cross-linked and non-cross-linked PP by a reactive extrusion process with a peroxide and a cross-linking agent (EP 0456342). Recently, new furfural compounds were introduced to obtain cross-linked PP (Polymer, 43, 1115; 2002). Further, Yu et. al. have prepared branched PP with 2,5-dimethyl-2,5-di(tert-butyl peroxy) hexane as initiator and Pentaerythritoltetraacrylate as cross-linking agent and stabilizer (Annual Tech. Conf. 2000; p-399). The transient recoverable strain measurements of modified PP indicate a increasing of elasticity due to the creation of branched structure.
PP with long chain branches were obtained using reactive extrusion in the presence of peroxydicarbonates (WO00108072) without any cross-linking co-agent where the type of peroxydicarbonates used controlled degree of long chain branches. Lu and Chung proposed a new method to prepare long chain branched PP with relatively well-defined molecular structure (Macromolecules; 35; 1999, p-8678). The chemistry involves a graft-onto reaction between malefic anhydride grafted PP and several amine group terminated PPs. The formed PP with long chain branches has an imide linkage that connects the PP backbone and each PP side chain.
Indeed, several researchers have successfully combined the positive properties of solid state chemical modification with the production of LCB-PP. Kim & Kim used the peroxide activation of four different coagents to produce LCB-PP samples whose melt rheological properties were characterized by melt flow index measurements (Adv. Polym. Technology; 1993; vol 12; p-263-269). Wang et. al. extended this work to detailed analyses of the steady shear viscosity and MWD of LCB-PP samples derived from reactions of PP with PETA (Ph.D Thesis, University of Waterloo; 1996). Analogous reaction products derived from TMPTA were prepared by Nam et. al. Who characterized melt-state rheological properties under oscillatory shear & extensional deformations (J. Appld. Polym. Sci? Vol 96; p-1793-2000; 2005). Continuing on this line of research, Borsig et. al prepared LCB-PP materials using divinylbenzene, hydroquinone & difurfuryl sulphide as co agents & characterized these derivatives by single-detector GPC & oscillatory shear rheometry (European Polymer Journal 44 (2008) 200-212) which has been updated currently.
Work on Hmelt strength-PP was further updated in a current publication (Journal of Applied Polymer Science, Vol. 110, 3727-3732 (2008)) where the Hmelt strength-PP was synthesized via silane grafting initiated by in situ heat induction reaction, in which pure PP powders without any additives and vinyl trimethoxysilane (VTmelt strength) were used as a basic resin and a grafting and cross linking agent, respectively.
WO/2007/100436 discloses a process of making Hmelt strength-PP via reactor polymerization of PP under multiple steps where process allow to combine the first quantity of polypropylene with the second quantity of polypropylene to form a bimodal polypropylene; wherein the percent by weight of the first quantity of polypropylene in the bimodal polypropylene composition is equal to or greater than 65 percent, and the ratio Mw,B/Mw,A is at least about 2.
WO/2008/006530 provides a polypropylene having good process properties, as low processing temperature and high process stability, in combination with good mechanical properties as high stiffness and high purity, i.e. rather low amounts of extractable fractions. The finding of the present invention is to provide a polypropylene with improved balance between mechanical and process properties by introducing a specific degree of short-chain branching and a specific amount of non-crystalline areas.
More precisely, the present invention is related to a polypropylene having a) xylene soluble (XS) of at least 0.5 wt.-% and b) a strain hardening index of at least 0.15 measured by a deformation rate dε/dt of 1.00 s″1 at a temperature of 180° C., wherein the strain hardening index (SHI) is defined as the slope of the logarithm to the basis 10 of the tensile stress growth function (Ig (ηε+)) as function of the logarithm to the basis 10 of the Hencky strain (Ig (ε)) in the range of the Hencky strains between 1 and 3.
Hmelt strength-PP is achievable by incorporation of long chain branching, which is made possible via electron beam (EB) irradiation process on commercial scale. The EB causes scission of the PP chains; the radicals so formed undergo controlled recombination, leading to LCB formation. Basell Pro-Fax PF 814, Borealis Daploy 130d have both the aforementioned long-chain branching structure, introduced by a post-reactor step, either by irradiation (Basell) or by reactive extrusion (Borealis), and are up to now the main materials successfully used to produce very low density foam. Modified PP is commercially available from Basell, Borealis etc that are used in foaming, thermoforming & extrusion coating processes. The electron beam method is carried out when PP is in solid state while other chemical modification is carried out when PP is in molten state. However, it is known that the use of high-energy radiation produces branching confined for the most part to the amorphous phase of the semi crystalline PP, since it is in this region that the segmental mobility and free volume are sufficient for macro radicals formed on irradiation to approach one another and form branches. In principle, branches can also be introduced onto the PP backbone by post reactor grafting reactions. Wang et. al did model for branched PPs by the reaction between a randomly functionalized PP and hexadecyl amine, a long chain alkyl amine that was used as a model molecule for a terminally functionalized PP. The constrained geometry catalyst (CGC) has also been found to be very useful for preparing LCB polyolefin. However, this is limited to laboratory scale only.
Even though most commercial Hmelt strength-PP is produced now by electron beam irradiation, the method of using peroxydicarbonates and reactive extrusion has recently regained interest to modify polypropylene. Another alternative to incorporate branching in PP may be through the recombination reactions in which PP molecules react with a polyfunctional (PFM) monomer, having more than two double bonds, in the presence of peroxide. It is well known that at relatively low concentration of peroxide the primary radicals generated will abstract preferentially the tertiary hydrogen, forming tertiary PP macro radicals that are unstable and degrade through β-scission reactions. However, addition of a polyfunctional monomer to the above system can convert some of the tertiary macro radicals to the more stable secondary macro radicals which tend to undergo recombination rather than scission owing to the randomness of these recombination reactions, PP chains may be extended, branched or even cross linked.
Lagendijk et. al investigated the efficiency of peroxydicarbonate (PODIC) for the modifications of PP. All PODIC modified samples show enhanced strain hardening, and PODIC with no-linear or large linear alkyl groups resulted in the modified PP with highest degree of branching with high degree of strain hardening. Wang et. al. used PFM i.e. Pentaerythritol triacrylate (PETA), and 2,5-dimethyl-2,5(tert-butylperoxy) hexane peroxide to produce branched PP and studied their melt flow properties by capillary rheometery and thermal properties. They discussed the effects of the concentration of peroxide and monomer on gel content. Low concentration of PETA and peroxide was suggested to minimize the formation of macro-gels. Monomers with different functionality were studied by Yoshi et. al.; the result showed that relatively shorter chain bifunctional monomers such as 1,4-butanediol diacrylate (BDDA) and 1,6-hexanediol diacrylate (HDDA) are better for improving the melt strength of PP.
To make PP having good mechanical properties and high melt strength, scientists have explored many methods such as blending, radiation cross linking and peroxide cross linking. Unfortunately, these methods have some disadvantages. For example, blending damages the properties of PP, especially the high temperature properties. Radiation cross-linking is limited by the material's thickness, and the process needs an inert atmosphere, which results in high cost and complicated manufacturing technology.
The peroxide cross-linking induces serious degradation of PP chains and even cross-linking. However, among the reported methods of preparing Hmelt strength-PP, direct solid state chemical modification of linear PP chains is still the simplest as well as economical and of course most appropriate for the applications compared to even currently developed silane grafting process for making Hmelt strength-PP as its process insight yet require in depth attention for commercial exploitation. Therefore, the current invention when particularly compared with exiting radiation and peroxide cross linked PP including silane grafting, the way of making branched/cross-linkable PP through simple melt grafting polyfunctional monomer in absence of any catalyst has various advantages, such as easy processing, low cost and capital investment, and favorable properties in the processed materials.
The grafting of coagent in this invention can be carried out by melt kneading of polymer with suitable device like single or twin screw extruder or in batch mode in one-step polymer processing. In this case, the extruder becomes the chemical reactor, which may involve high temperature, high viscosity, etc. With a linear chain, two approaches allow the transition of the flow regime for the same deformation rate: an increase of molecular weight or the grafting of long branches. The grafting is preferable to limit the increase of the shear viscosity. The branched polypropylenes show strain hardening in elongational flow of polypropylene and high melt strength. According to Gaylor, the Hmelt strength-PP is characterized by a bimodal molecular weight distribution, wherein the higher molecular weight fraction contains branched polymer.
The melt strength and elongation behaviors of modified PP are strongly related to the degree and length of LCB. The length necessary for a branch to behave as a long chain branch is 2Me (Me: MW between entanglements. As compared to various known techniques, melt rheology has been found to provide significant evidence of incorporation of long chain branching in the polymer chains. Hence, rheological techniques are Prevalent to detect the presence of LCB, though it is an indirect method. Therefore in the current invention dynamic rheometer is used to evaluate melt rheological characteristics of modified samples which ultimately provide evidence of strain hardening & high melt strength resulting from the incorporation of long chain branching.
In the past decade, many researchers have investigated LCB polyolefin by rheological method, but most studies focus on PE or model polymers and only a few are about LCB-PP, because LCB-PP is difficult to be obtained and the degree of LCB is very low. When PP is modified by peroxide and PFM, the reaction and the product components become very complex. Degradation reaction makes the MW to decrease, grafting reaction introduces short chain branching (SCB) structure, blanching reaction introduces LCB structure and gel will be produced if cross linking reaction can happen. Such complex reactions as well as the complex products make the investigation on LCB-PP very difficult and quite challenging.
Therefore, in the current approach efforts were made to make the process more simple & eco-friendly. More precisely, process is optimized in such a way that LCB-PP can be achieved via melt grafting of PFM either PETA or TMPTA under optimum process condition without using any catalyst. More particularly, current process primarily focused how to control kinetics of grafting process of acrylic based monomer coagent on polyolefin matrix so that during extrusion homo polymer formation should be strictly prohibited using normal dose of stabilizer/s either in nitrogen or in air environment subjecting a optimum predispersion innovative step in term of time & temperature prior to extrusion primarily to facilitate perfect dispersion & control branching to improve melt strength of either PP or PP-ICP copolymer via direct grafting process avoiding master batch situation as well as noninclusion of any peroxy radical forming catalyst which is mostly common in known prior art, for example, EP1952970 A1.
Therefore, based on current status reviewed above on the aspects of known prior art, process chemistry & structure—property relationship for LCB-PP/Hmelt strength-PP, there is yet a gap to refine process in term of process economy, efficiency & minimization of process steps which ultimately should qualify for commercialization. Overall, process should be smart enough to increase processing efficiency, minimizing off spec. products & thereby decrease the processing cost. Accordingly, it would be desirable to produce a high melt strength polypropylene by more convenient and less costly means.